时隙ALOHA协议仿真

第1页共39页时隙ALOHA协议仿真潘鹏飞（陕西理工学院物理与电信学院电子1103班，陕西汉中723000）指导教师：吴燕摘要：时隙ALOHA是应用于无线通信系统中的一种协议，时隙AL0HA使用了各种控制算法以保证系统的稳定性，在比较三种常用网络仿真模型的基础上，分析了时隙ALOHA仿真结果及应用于通信系统中的性能优点。给出了MATLAB仿真平台下实现时隙ALOHA控制算法的流程图，编写了MATLAB代码对时隙AL0HA的伪贝叶控制算法性能进行协议性能测试及仿真结果表示。关键字：时隙；ALOHA；仿真；MATLAB陕西理工学院毕业设计第2页共39页SimulationofslottedALOHAprotocolPanPengfei“(Grade11,Class03,MajorElectronicInformationEngineering,InstituteofphysicsandTelecommunicationsDept.,ShaanxiUniversityofTechnologyHanzhong723000,Shaanxi)”。Tutor:WuYanAbstract:SlottedALOHAisusedinawirelesscommunicationsystem,slotALOHAusevariouscontrolalgorithmtoensurethesystemstability,inthecomparisonofthreekindsofcommonlyusednetworksimulationmodelbasedon,analyzestheslottedALOHAsimulationresultsandapplicationincommunicationsystemperformanceadvantages.GivestheMATLABsimulationplatformtoachieveslottedALOHAcontrolalgorithmflowchart.WritethematlabcodeforthetimeslotALOHApseudoBeileafcontrolalgorithmperformanceprotocolperformancetestingandsimulationresults.Keywords:Slot;ALOHA;Simulation;MATLAB陕西理工学院毕业设计第3页共39页1引言························································································································42多地址接入协议发展状况····························································································42.1多地址接入协议概述··························································································52.2多址接入协议分类·····························································································52.2.1非竞争多址接入协议·················································································72.2.2竞争多址接入协议····················································································72.3多址接入协议仿真模型·······················································································72.3.1仿真系统模型··························································································72.3.2业务源模型···························································································102.3.3协议评价指标························································································103ALOHA协议的基本原理···························································································103.1时隙ALOHA的基本原理··················································································123.2时隙ALOHA的程序流程图···············································································133.3时隙ALOHA系统模型·····················································································143.3.1时隙ALOHA马尔科夫链系统模型·····························································143.3.2离散时间系统模型··················································································143.3.3蒙特卡罗法···························································································154MATLAB仿真软件的介绍·························································································154.1时隙ALOHA协议在MATLAB中的实现·····························································164.1.1随机数的生成························································································164.1.2信道状态的判断·····················································································164.1.3为贝叶斯调整算法实现············································································164.2时隙ALOHA协议仿真结果分析·········································································17结论························································································································18参考文献··················································································································21附录A:····················································································································21附录B:····················································································································33陕西理工学院毕业设计第4页共39页1引言随着无线通信的不断普及，无线移动环境中的多址接入协议正在引起人们更多地关注。在此条件下，更应当关注协议的稳定性和鲁棒性。在无线移动环境中，多址接入协议面临如下四点挑战：隐终端问题，即两个或多个终端由于高山、建筑物等的遮挡而不在彼此的通信范围内，但却在同一基站的通信范围内；远近效应问题，远端的用户要比近端的用户信号有更大的衰落；无线信道中的多径效应和阴影衰落问题；由于相邻小区共用同一频率而导致的共道干扰问题。对于一种协议来说，同时处理好上述问题是比较困难的，甚至是相互冲突的，因此，只能在设计时进行折中处理，折中的程度取决于使用环境，以及特定的需求。设计开发新的协议或对已有协议进行改进，都需要对其性能进行测试和评价。测试的方法一般有两种：一种是在实际网络环境中进行测试，即实验；另一种是在计算机仿真环境下测试。在实际环境下测试能够得到相对真实的数据，但由于现代通信与信息系统往往规模很大，系统很复杂，构造高度相似的物理模型经济成本和社会成本都很高，因而进行对大规模的测试几乎是不可能的，而且其测试结果也往往难于重现。目前，计算机仿真的方法在通信网络技术的研究中得到了广的应用，因为其具有很好的可控制性、可重现性、可扩展性。利用比较成熟的计算机仿真软件，可以近乎真实地模拟网络环境，可以在各个层次上模拟网络的运行效果。因此，在仿真软件的帮助下，我们可以很好的模拟各种接入控制协议，并分析其性能。在此基础上，针对发现的问题提出理论改进，然后在仿真平台上实现改进理论，并通过性能比较分析来验证改进效果。这种低成本、高效率的计算机仿真的方式势必成为研究接入控制技术的首选。ALOHA作为一种通用的MAC协议广泛应用于多个用户终端竞争同一个媒质的情况。现今，GSM系统，卫星通信，无线局域网络的试验网络及基于无线认知网络的试验网络中均采用时隙ALOHA协议作为媒体接入控制协议以实现对信道的共享接入方式。但时隙ALOHA本质上是不稳定的，当输入流从0开始增加时，信道吞吐量随着负载流的增加而增加，当输入流到达某一门限值时，系统吞吐量到达最大值。当输入的载荷超过信道容量后，随输入流量的增加冲突也随之增加，重复发生的碰撞将浪费部分系统的宽带，从而使系统吞吐量随着生成载荷流的增加而迅速下降。为解决时隙ALOHA的稳定性问题，各种控制算法被提出。为对算法性能进行评估，将所有这些算法应用到实际系统中进行测试是不现实的，必须通过软件仿真方式对算法性能进行评估和测试。网络仿真技术是一种通过建立网络设备和网络链路的统计模型，并模拟网络流量的传输，从而获取网络设计或优化所需要的网络性能数据的仿真技术。由于仿真不是基于数学计算，而是基于统计模型，因此统计复用的随机性被精确地再现。网络仿真技术具有以下特点：（1）全新的模拟实验机理使其具